1. Field of the Invention
The present invention relates to the fabrication of integrated circuits, and more particularly to a wafer carrier with a low profile that reduces fluid flow obstruction, decreases processing time, and increases wafer yields.
2. Description of Prior Art
Integrated circuit devices are produced on semiconductor wafers where each wafer can produce a multitude of integrated circuit devices. Two long standing goals of wafer processing are: (1) to increase the yield of properly functioning devices obtained from each wafer; and (2) to decrease wafer processing time.
In processing wafers, wafers are subjected to a multitude of different processing steps. Wafer carriers are used to transport the wafers to these different processing areas. Often, the wafers are not removed from the wafer carriers while the wafers are subjected to certain processing steps such as cleaning and drying steps. It is desirable to process wafers while in a wafer carrier not only because the wafer carrier provides support for the wafers, but also because doing so reduces handling of the wafers which can result in the undesirable outcomes of breaking and/or contaminating the wafers. It is well known in the art that contaminating a wafer will very likely reduce the yield of properly functioning devices obtained from a wafer. Thus, it is desirable to have a wafer carrier that can used to process the wafers.
While this is true, leaving wafers in a wafer carrier during processing can create a number of problems in of itself. For example, in processing wafers, it is known in the art that the presence of liquid on a wafer will decrease the yield of that wafer. However, because removing contaminants is crucial to obtaining properly functioning devices, wafers are subjected to a rinsing step. After rinsing, the liquid must be completely removed from the wafer surface or the affected devices will fail. Removal of this liquid is performed at a drying step. For the reasons stated above, the wafers are often in the same wafer carrier both during the rinsing step and the consecutive drying step. Often, despite going through the drying step, a certain amount of liquid will get trapped between the wafer and the wafer carrier at those points where the wafer contacts the wafer carrier. The greater the size of the contact area present between the wafer carrier and the wafers, the greater is the amount of liquid trapped. This trapped liquid is undesirable for two reasons. First, the area of the wafer that remains wet can not be used to make properly functioning devices. This is know in the art as edge exclusion and results in lower yields. Second, processing time will be increased because the more liquid that is trapped between the wafer carrier and the wafers, the longer it will take to substantially dry the wafers. Thus there is a need for a wafer carrier that reduces the area of contact between a wafer carrier and the wafers while still properly supporting the wafers.
Currently, there are no wafer carriers that effectively minimize the number and size of these contact points. Existing wafer carriers either have four supporting members that contact the wafers or the supporting members are designed so as to contact a substantial area of the wafers being supported thereby.
Another problem that arises in processing wafers while in a wafer carrier is that the wafer carrier can obstruct the flow of fluid over the wafer surfaces. The unobstructed flow of processing fluids over wafer surfaces is essential to efficient and effective wafer production. Depending on the particular processing step involved, obstructed fluid flow can result in contaminants not being removed from the wafer surfaces and/or increased processing times. These problems can arise in a number of processing steps, including rinsing and chemical treatment. Moreover, many of the processes necessitating fluid flow take place at elevated temperatures and in corrosive chemical environments. Thus there is a need for a wafer carrier that is as non-obstructive as possible with regard to fluid flow while remaining structurally sound during rigorous thermal cycling and chemical exposure.
Currently, plastic “wafer baskets” are used to carry and process wafers. Wafer baskets are bulky and are not fluidly dynamic. As such, these “wafer baskets” obstruct a substantial amount of fluid flow, resulting in increased processing times and/or decreased yields.
Yet another problem that arises in processing wafers in currently available wafer carriers is that the processing tanks must be large enough to accommodate not only the wafers, but also the additional size of the wafer carrier. This leads to bulkier tanks and processing equipment which is more expensive to both build and operate. Thus, there is a need for a structurally compact wafer carrier that can structurally support a plurality of wafers.